Field of the Invention
The present disclosure relates to a light emitting device.
Description of the Related Art
Light emitting devices including, in combination, a light source, and a wavelength conversion member, which is capable of emitting light with hues different from the hue of the light source when excited by the light from the light source, and thus being capable of emitting light of various hues owing to the principle of the mixture of colors of light, are being developed. In particular, light emitting devices composed of a light emitting diode (“LED”) combined with a fluorescent material are increasingly and widely utilized, for example, as lighting systems or as backlights for liquid crystal displays. For instance, in a light emitting device that emits white mixed color light, a fluorescent material that emits light at short wavelengths, such as blue-green, green, and yellow-green, and a fluorescent material that emits light at long wavelengths, such as orange and red, may be combined, for example, to allow liquid crystal displays to have an improved color reproduction range and lighting systems to have an improved color rendering.
As fluorescent materials with less reduction in luminance when excited at high energy, fluorescent materials that have a nitrogen-containing inorganic crystal as a host crystal in the crystalline structure, such as sialon fluorescent materials, oxynitride fluorescent materials, and nitride fluorescent materials, have been proposed. Of these, as examples of nitride fluorescent materials, Eu2+-activated red fluorescent materials having CaAlSiN3 as a host crystal (hereinafter referred to as “CASN fluorescent materials”) and (Sr,Ca)AlSiN3:Eu, which is a CASN fluorescent material in which a part of Ca is replaced with Sr (hereinafter referred to as “SCASN fluorescent material”) is known. CASN fluorescent materials and SCASN fluorescent materials have a peak emission wavelength in a range as wide as from 610 to 680 nm. The half bandwidth of these light emission spectra is from 75 to 95 nm.
As an example of nitride fluorescent materials having a narrow half bandwidth of 70 nm or less, SrLiAl3N4:Eu (hereinafter referred to as “SLAN fluorescent material”) has recently been proposed. The peak emission wavelength of this compound is around 650 nm (see, e.g., WO 2013/175336 A1 and Nature Materials, NMAT4012, 2014).